The subject invention related generally to holograms for center-high mounted stop lights (CHMSL) for vehicles, and more particularly to holograms that efficiently meet the required transparency, brightness and angular coverage and to exposure techniques for recording such holograms.
In the United States, Federal regulations require CHMSLs on most motor vehicles in addition to the standard “tail light” stoplights on the rear of the vehicle. CHMSLs are intended to maximize the visibility of the “brake lights” to drivers behind the CHMSL-equipped vehicle, and are usually mounted on or above the rear window of said vehicle.
Pre-CHMSL high-mounted stoplights found in the prior art comprise a standard lenticular lens and an incandescent bulb or light emitting diode (LED) mounted in a housing that is usually secured near the top or bottom of a motor vehicle's rear window. However, such stop light units have bulky housings that partially obscure the rearward vision of the vehicle's driver. Additionally, limitations on the aesthetic and functional design of the automobile are imposed. Some other center high-mounted stoplights found in prior art have been also integrated into automobile body features such as trunks, airfoils, and roofs, which, to a limited degree, substantially reduce or remove the driver's vision problem. However, such high-mounted stoplights are unnecessarily complex and may impose further limitations on the functional and cosmetic design of vehicles.
There were attempts to make transparent CHMSL based on transmission holograms. The illumination lamp was bulky and there was probability that the light beam could be blocked from inside the car. A holographic CHMSL based on a single hologram is known. Such a holographic CHMSL, couples out the light trapped in the substrate by edge lit. This geometry has a well-known disadvantage of significant aberrations and dispersions intrinsic to this type of holographic optical system, and resulted in a non-uniform output beam.
One benefit of the subject invention is high light throughput.
Another benefit of the subject invention is high transmission of implemented holograms that don't create obscuration of the driver's rear view.
Also, flexibility in terms of direction and shaping the beam emitting from the CHMSL is yet another benefit.
Another benefit of the subject invention is low aberration and distortions that allow images to be included in CHMSL.
Another benefit of the subject invention is more uniform light coupled out to the viewer.
Another benefit of the subject invention is flexibility in recording and using either reflection or transmission SGWH.
Still another benefit of the subject invention is adjustability to the different LED, robustness and environmental stability.